Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS


News 09-10 (No.262)

Issued : October 25, 2009

[ Japanese Version ]

"Obihiro no Mori" New Ice Rink

by Akira Ono, Masaya Uchida

<< The Project's Architectural, Ventilation and Acoustical Designs >>

Hokkaido's Obihiro city is home to many of Japan's most famous speed skaters, including Hiroyasu Shimizu, gold medalist at the 1998 Nagano Winter Olympics, and 10 Japanese speed skaters who competed at the 2006 Torino Winter Olympics. In September, 2009, the city welcomed the opening of a new indoor speed skating rink in Mori no Undo Koen, an expansive 406.5 ha (1,004 ac.) park devoted to indoor and outdoor athletic facilities. This proximate grouping of athletic facilities is the largest of its kind in Hokkaido and has 12 indoor and outdoor facilities, including the new indoor ice rink, an indoor gymnasium, a baseball stadium, swimming pools and an outdoor athletic track and field, as well as indoor and outdoor spaces for other sports.

Prior to the completion of the new indoor speed skating ice rink, the many Japanese speed skaters who converge on Obihiro yearly for competition training relied on outdoor ice rink facilities. With the opening of the new ice rink, the speed skating training season can be lengthened. Both athletes and fans hope that the longer training season will increase Japan's chances of earning a medal at next year's Vancouver Winter Olympics.

Interior View
Interior View

Exterior View (model)
Exterior View (model)

>> Regulation Dimensions and a Design that Maximizes Use

Mori no Undo Koen's new indoor speed skating ice rink is Japan's second indoor ice rink built to the regulation dimensions for speed skating competitions. (Japan's first indoor regulation indoor speed skating ice rink was built for the Nagano Olympics and now operates under the name "M-Wave, Nagano Olympic Memorial Arena." The Mori no Undo Koen rink's dimensions measure 15 m. wide and 400 m. long, and the rink has a double-lane track. These specifications match the requirements stipulated by the Japan Skating Federation. In addition, the infield (the area that occupies the center of the oval) was designed and constructed so that the rink can be used as a multipurpose venue for other sporting activities and events during speed skating's summer off-season.

>> Architectural Design and Acoustical Design

The horizontal footprint of the ice rink building has the same oval shape as the ice rink. The ceiling ventilation diffusers supply air to the interior of the building so that the air flows in the same direction as speed skaters using the rink. The corners of the building follow the curved, semicircular shape of the rink, aiding the air flow. According to persons involved in this aspect of the project, when skaters skate through these curves, rotational air flow is created that provides the skaters with some helpful tailwind. The ventilation design helps skaters improve their skating times and makes the new ice rink very popular among skaters.

From the acoustical design perspective, the curved corners of the walls might cause sound reflections to produce undesirable sound focusing. To prevent this phenomenon from occurring, our design developed the prevention strategy of making the entire surfaces of the corners sound absorbing. By implementing this strategy, sound focusing problems were successfully avoided.

Infield's Loudspeaker (View From the Long Distance)
Infield's Loudspeaker (View From the Short Distance)
Infield's Loudspeaker

<< The New Ice Rink's Sound System Design >>

A key objective of the new ice rink's sound system design was to deliver clear speech amplification to both the infield and the spectator seating. Due to the very nature of this facility's purpose, its floor surface, which is primarily covered with ice, is necessarily a sound reflecting surface. The only large surface area for the addition of sound-absorbing measures was limited to the ceiling, while the building's large spatial volume meant that we could expect the space to exhibit a long reverberation time.

For our sound system strategy, we designed a layout of dispersed, multiple loudspeakers, with the coverage area of each speaker limited to a small area. Limiting the coverage area of each speaker enables control of the output level of each speaker and, therefore, we were able to reduce the generation of excessive sound reverberation. In addition, we positioned the speakers so that, when amplified sound reflects off of the infield's floor, the sound will travel in the direction of the sound-absorbing ceiling, rather than toward the sound-reflecting sidewalls of the arena. This strategy also prevented the creation of an overabundance of sound reflections.

Specifically, for the infield's loudspeakers, we suspended 20 units at dispersed locations from a catwalk that hangs below the ceiling around the circumference of the infield, and we placed the front of each speaker at an angle of about 60 degrees from horizontal. (The coverage areas of the speakers facing each other overlap slightly at the center line of the infield.) Similarly, we suspended the speakers for the spectator seating areas from a catwalk above the seating, placing 9 units in dispersed locations.

For all of the units, I chose a type of speaker with a large horn that would have stable directionality across a far distance. This decision ensured the success of the sound system design.

In the sound tuning, major concerns are preventing howling feedback noise and controlling low frequency sound. During the ice rink's opening ceremonies, infield areas that had loudspeaker coverage overlapped with areas, became the "stage" where people spoke and delivered speeches using microphones. So I paid especially intense attention to eliminate sound frequencies that would cause howling feedback between the microphones and the suspended speakers. For low frequency sounds, I concentrated to achieve the proper balance between clarity and quality in the sound tuning, because speaker directionality does not control low frequency sounds. As a result, the ice rink's amplified sound both retains natural and warm tones and can be clearly heard by listeners throughout the building.



A Look at Anti-vibration and Sound Isolation Structures from "the Bottom Up"
-- How countries without earthquake concerns build to mitigate vibration --

by Dr. Keiji Oguchi

Nagata Acoustics is a participant in several European concert hall projects now being constructed. In the February, 2007 issue of this newsletter, I introduced readers to our use of 1/10 scale models on two of our European projects. In this article, I will turn my focus to our strategies for ensuring "quietness" in the hall interiors of two of our European projects. Readers who are familiar with the building methods used in earthquake-prone places such as Japan will surely notice some differences between practices in earthquake-prone locations and those used on these European projects.

In this newsletter's series on sound isolation design, we previously discussed the methods we use to achieve the goal of isolating concert halls from noise and vibration generated by the environment outside concert hall buildings. Typically, we install anti-vibration materials characterized by cushiony resilience under the floors, behind the walls and above the ceilings of rooms, placing these materials in between the concert halls and their supporting anti-vibration and sound isolating structures. In major Japanese cities such as Tokyo, where trains and subways run ubiquitously in all directions and where maximum use must be made of scarce land resources, the inclusion of this kind of anti-vibration and sound isolation measure can be considered a standard part of concert hall acoustical design.

Fig. 1 Concert Hall, Helsinki Music Center
Fig. 1 Concert Hall, Helsinki Music Center

Fig. 2 Floating floor of the concert hall, Helsinki Music Center
Fig. 2 Floating floor of the concert hall,
Helsinki Music Center

<< Helsinki Music Center Project >>

We featured the Helsinki Music Center project in the November, 2000 issue of this newsletter. This project includes a 1,650-seat concert hall that will be the home hall of both the Helsinki Philharmonic Orchestra and the Finnish Radio Symphony Orchestra(Fig.1), and a new facility to house Sibelius Academy Music University.

Along the western end of the project site runs Helsinki's Mannerheim Street and a tram line. Before beginning our design work, we studied the site and determined that our design would need to include a strategy to mitigate the effects of structure-borne noise from Mannerheim Street and the tram line on the concert hall and other rooms. On the side of the building closest to Mannerheim Street, we located the orchestral, organ, chamber music and vocal rehearsal halls, as well as the "black box" space for experimental performances, and we adopted a "box-in-box" floating structural design for each of these rooms.

The construction workflow for the box-in-box structures begins with building the floating floor of the inner box, then adding the pre-cast concrete walls, followed by spraying shotcrete on the ceilings. As I write this article, the construction work of the inner boxes for the box-in-box structures of the rehearsal halls on the west side of the building is approaching completion. In this part of the completed building ample space can be seen below the flooring of the inner boxes and we can easily confirm the state of the resilient supports installed as an anti-vibration measure.

In Japan, the substructure below floors of box-in-box rooms typically has anti-seismic stoppers that were developed to prevent sideway movement of structures during earthquakes. Helsinki does not experience earthquakes and, therefore, anti-seismic stoppers are unnecessary there. At the Helsinki Music Center, narrow columns topped with foamed polyurethane elastomer provide the structural support for the inner boxes of the box-in-box structures. To readers who, like me, are used to seeing earthquake-resistant structures made of thick columns and beams implemented to support concrete building elements, the appearance of the Helsinki substructure may not intuitively inspire strong confidence, but this column thickness does adequately provide vertical support for the weight it bears.

Compared with the rehearsal halls, the concert hall is located at a slightly farther distance from the tram line (40 m. when measured as a direct line through the building). Nevertheless, we determined the risk of the hall space being affected by structure-borne noise to still be considerably high, and we adopted a floating foundation structural design for the concert hall's main floor, including the stage(Fig.2). Because of the concert hall's vineyard configuration, the hall's floor is divided into a complex design of sections or blocks. To prevent horizontal shifting of these sections during construction, the same kind of rebar configuration that is used for seismic resistance was embedded in the structural design of this part of the project.

Fig. 3 Elbphilharmonie Hamburg
Fig. 3 Elbphilharmonie Hamburg

Fig. 4 Under the inner box of Kleiner Saal, Elbphilharmonie Hamburg
Fig. 4 Under the inner box of Kleiner Saal,
Elbphilharmonie Hamburg

Fig. 5 Under the inner box of rehearsal room, Shanghai Conservatory of Music
Fig. 5 Under the inner box of rehearsal room,
Shanghai Conservatory of Music

<< Elbphilharmonie Hamburg Project >>

We featured the Elbphilharmonie Hamburg project in the December, 2004 issue of this newsletter. This construction project includes a large hall and small hall (approx. 2,150 seats and 550 seats, respectively), condominiums and a hotel in a spectacular high-rise structure built on a site that was most recently occupied by a warehouse(Fig.3). The new structure extends into Hamburg's Elbe River harbor. To isolate the concert halls from noise sources outside the building, and to provide sound isolation both between the halls and between each of the halls and the building's condominiums and hotel, we adopted a box-in-box design strategy for this project's halls.

Partially surrounded by water, the Elbphilharmonie Hamburg building exterior environment will include large ocean freighters traveling into and out of Hamburg Port through a waterway adjacent to the south side of the building. Also, passenger ocean liners, such as Queen Mary II, are expected to tie up on the east side of the building, where passengers will disembark to spend time at the city. Ocean-going vessels blow their distinctively low-pitched horns when traveling from the port out to the ocean.

To isolate the concert halls from the low-pitched horn blasts of ocean-bound vessels, we did not use the typical cushiony anti-vibration material. Instead, we implemented building isolation springs that provide excellent and extended sound isolation performance for low frequency sound because they can be set to low natural frequencies. Specifically, this box-in-box design has an outer-box constructed using 200 mm-thick concrete inside of which is another box, also built using 200 mm-thick concrete. The springs are installed inside the outer box as the supports for the inner box. The hall's interior is built and finished inside the inner box. The natural frequency of vibration used for this design is 3.5 Hz.

The springs used in this design can be compared to the seismic isolating mechanism used in a seismic isolation structural design. However, because seismic isolation mechanisms are designed to dampen the effects of horizontal shaking, they are comparatively stiff in the vertical direction, while the Elbphilharmonie Hamburg building's anti-vibration springs are compliant in both the horizontal and vertical directions. For this reason, the building isolation whose natural frequency of less than 5Hz has never been practiced in earthquake-prone Japan.

At present, the small concert hall (the "Kleiner Saal") is the focus of construction activity at the Hamburg project. Like in Helsinki, the space beneath the inner box of the Kleiner Saal is accessible for confirmation of the design implementation (Fig. 4). Because the Kleiner Saal interior is still under construction, temporal support poles can be seen in the space below the inner box. When the hall's construction is complete, the hall will be supported entirely by the springs. An example of another example that has an entire room supported by springs can be seen in the photo of Fig. 5. The use of springs in the box-in-box design of these halls effectively prevents noise and vibration in the concert hall interiors.



The Center for Shanghai Symphony Orchestra with Concert Halls Project

by Dr. Yasuhisa Toyota

Exterior Perspective Drawing
Exterior Perspective Drawing

Interior Perspective Drawing
Interior Perspective Drawing

Shanghai Symphony Orchestra, which was founded in 1879 and has the distinction of being the oldest orchestra in Asia, celebrates its 130th anniversary this year. Even when compared with the most venerable orchestras in Europe and the United States, only the Vienna Philharmonic, founded in 1842, is older. The Shanghai Symphony Orchestra has a longer history than the Berlin Philharmonic (founded in 1882), the Amsterdam Concertgebouw (founded in 1888), the Boston Symphony Orchestra (founded in 1881) or the Chicago Symphony Orchestra (founded in 1891). In Japan, the establishment of the first orchestra came much later, in 1926, with the establishment of the New Symphony Orchestra (which later became the NHK Symphony Orchestra).

Shanghai Symphony Orchestra performs its regular subscription concerts at the Shanghai Grand Theatre, completed in 1998. However, for its daily practice and rehearsal sessions, the orchestra uses an old, wood-framed structure that belongs to it exclusively, but that provides a poor acoustical environment inappropriate to the needs and performance level of the orchestra.

To address the situation of the orchestra's current practice and rehearsal facilities, in June, 2008, the City of Shanghai decided to fund the design and construction of a rehearsal hall dedicated exclusively to use by the Shanghai Symphony Orchestra. Immediately thereafter, the city proceeded to put its decision into action by holding a design competition to select the project architect. Local Shanghai architects, Japanese and U.S. firms participated in the design competition, which resulted in the project being awarded to Japan's Arata Isozaki & Associates.

From the inception of this project, the project's two sponsors, the City of Shanghai and the Shanghai Symphony Orchestra, retained Nagata Acoustics as their acoustical consultant. In this capacity, we served as acoustical advisor during the design competition stage and are continuing our acoustical consulting responsibilities through the design and construction management phases of the project.

The new rehearsal hall's planned location places it conveniently in a central part of the city, next to the Shanghai Conservatory of Music, which is also known for its long and laudable history. From the start of this project, the design approach has been to enable the rehearsal hall to also be used for small scale concerts. Initially, the design aimed to provide seating for an audience of about 800 to 900, but as the design progressed, the scale became increased to 1,200 seats. The accompanying exterior and interior perspective drawings reflect the 1,200 seat design.

Currently, the project has completed the schematic design phase (equivalent to Japan's basic design phase plus a portion of the design development). We will now begin development of the detailed designs while, in the meantime, construction of the building foundation started in this August, 2009 at the construction site. Construction of the structure is planned to be completed before Expo 2010.


Nagata Acoustics Inc.

(Tokyo Office)
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Bunkyo-ku, Tokyo 113-0033, Japan
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E-mail: info@nagata.co.jp

[ Japanese Version ]